Process for producing titanium



Feb. 26, 1957 R. s. DEAN 2,783,192

PROCESS Foa PRODUCING TITANIUM Filed sept. 22, 1954 United States Patent O PROCESS FOR PRDUCING TITANIUM Reginald S. Dean, Hyattsville, 'lV/Id., assigner to Chicago Development Corporation, Riverdale, Md.

Application September 22, 1954, lSerial No. 457,796

3 Claims. (Cl. QAM- 10) K This invention relates to `processes for the production of titanium. It has for its object ,the production of pure titanium by a process which combines a procedure for producing an impure titanium having a specic distribution of the impurities in the mass with .the anodic dissolution of the titanium from such a mass, leaving the impurities in a form readily separated from the `electrolyte and reducing the dissolved titanium by cathodic action.

I am fully aware of the prior art in reducing titanium oxide to titanium in admixturc with the oxide of `the reducing agent such as calcium or magnesium. I `am likewise familiar with two-step reduction of titanium dioxide to metallic titanium by reduction to an intermediate oxide, for example by carbon,.and the further reductionVto metal'by a more expensive reducing agent such as magnesium. I am also familiar with procedures `for separating the reduced titanium from the other ,products of reduction, including acid solution of the latter .and separating the titanium from a reduction mixture containing a large excess of magnesium by Vimpingement in accordance with my copending application Serial No. Y

421,420, filed April 6, 1954. Y

For the practice of my present invention, `the Iimpure titanium mass may be most lsimply and economically produced by agglomerating and separating the titanium lfromthe reduction mass of metal and alkaline earth oxide and then melting the crude titanium. The ,agglomeration of the titanium in the reduction product with magnesium is preferably accomplished by adding a suitable flux such as barium chloride. Other non-oxidizing jhalide iluxes may be used. The amount of flux added is .only-enough to produce a suitable surface relationship vbetween .the titanium metal and magnesium oxide so that with `mechanical `work Vthe titanium will agglomerate excluding the slag. This is from 525% by weight `of ,thetitanium in the mass. This sort of procedure has its counterpart in the so-called Krupp-Renn process in which iron ore is mixedwith carbon and ,limeand .then ymechanically treated to agglomerato the reduced iron and separate it from the slag. The mechanical working necessary to agglomerate the titanium may be accomplished in a rotating tube at l000 C. with or Without balls or rods. Such tube must, of course, be kept free from active gases. Alternatively, the agglomeration may be performed in a closed tube or sheath and in this instance the product may be a consolidated titanium mass suiiiciently free from slag to be used directly as an anode without the melting step. Such an anode has the impurities in the form of fairly large slag masses which do not form anode slime but provide an anode residue which separates readily from the electrolyte. It will be clear, however, that other steps than those described may be used. It is important only that the titanium metal be separated as far as possible by simple mechanical means from the alkaline earth oxides and other impurities.

In a preferred form of my invention the agglomerated titanium is then melted and Vallowed to solidify slowly.

2,783,192 .Patented Feb. 25, 1957 Under these circumstances it is well known that titanium free from suspended impurities will crystallize at the cooling surface, and that the inclusions will be segregated in the last metal to solidify. This is not new, and I do not claim it. Ingots of titanium with =a core of impurities have heretofore been produced. Such ingots have not, however, .been 'useful because even if the impure core were mechanicallyremoved there would still remain oxygen dissolved in the solid titanium. My invention makes the 'first `practical 1use -of such ingots because vby using them as anodes in a fused chloride electrolyte I causethe dissolved oxygen to diffuse into the core which I remove from .the electrolytic bath before it mechanically disintegrates. Here .again Ido not claim the refining procedure in which oxygen diffuses into the discarded part of the anode. This has been done by others. This embodiment of my V.invention resides in fthe 'production of a cored titanium anode and the electrorefining :of such an anode Aonly tothe extent that the core;does not disintegrate.

This combination of steps in producing pure titanium from `its oxide is 4highly important from a practical standpoint. In the known procedures 'the impurities in the titanium beingmore or less uniformly distributed appear during ythe electrolysis as anode-slime. The separation of this slime from `the electrolyte is very diiicult. With my `inventionnosuch slime is formed. The absence of anode slime permits the use of an improved electrorening process in accordance With'which `unidirectional 4direct current is passed :through a suitable fused salt bath electrolyte from one Vto .the :other of two electrodes of crude titanium, and rperiodicallyreversing the direction of the current. Under these vconditions .pure titanium is formed adjacent -both electrodes, and falls to the bottom ofthe bath. It .will be clear that anode 4s'lime would contaminate the titanium, and my present invention, which Apermits the separation of the anoderesidue, is therefore particularly applicable to this process.

Having described my invention, which fresides .in the steps of producing a tit-anium mass with the insoluble impurities segregated Vin a .suitable mannerand then electrorening the mass, l will now illustrate vit by several examples.

Example] actionfat 1000* QC. Thetitaniumpellets -formed vare sepa- .rated from the rpulverulent slag by known means such ,asscreening Ithen'meltthe titanium pellets. The molten titanium is poured into a mold. The mold is lined with magnesium oxide and insulated to produce slow cooling. The mold is cylindrical and 3 inches in diameter. A microscopic examination of the ingot shows that all of the insoluble impurities are segregated in a core l inch in diameter. The outer section of the ingot contains 3% oxygen. It will be obvious that such an ingot is worthless by the standards of the known art. I now take this ingot and make it'an anode in a bath of fused sodium chloride at 850 C. I provide a titanium cathode, and pass a direct current through the cell at a current density of 300 amperes per square foot on both anode and cathode. The cell is maintained in an inert atmosphere, and 3% titanium dichloride is added to the electrolyte. I continue the electrolysis until the diameter of the anode is slightly more than l inch. l then remove the cathode and the anode and cool them in an inert atmosphere. The metal on the cathode is washed with hot Water and found to be 99.9% titanium. The anode core is added to another melt for the formation of anodes. The impurities in the anode are not thereby increased since the separation of insoluble impurities in the melting vand casting operation is constant.

Example l1 I proceed as in Example I to make a number of ingots. In this example both electrodes are the crude titanium ingots. The electrolyte temperature and current density are the same as in Example I. The current, however, is reversed every 2 minutes. The titanium metal formed drops to the bottom of the cell. The electrolysis is continued as before until the ingots are slightly more than 1 inch in diameter. The titanium recovered from the bottom of the cell after water washing is 99.9% pure.

The above procedure is carried out in an electrolytic cell such as shown in the appended drawing, in which:

Figure l is a diagrammatic representation of the cell, and

Figure 2 is an enlarged cross-sectional view of one of the electrodes used in the cell.

In Figure 1, 1 is a sillimanite pot, 8 is an inverted nickel bell adapted, when the cell is in use, to dip into a body of fused molten salt electrolyte in the pot 1. Electrodes 2, 2 are massive titanium bars, three inches in diameter, and 3, 3 are packing glands for the electrodes. 4 and 5 are a helium outlet, respectively, for maintaining an atmosphere of helium in that portion of the bell 8 not occupied by electrolyte. 7, 7 are insulating washers for insulating bell 8 from the packing glands 3, 3 through Which-as indicated in the drawing-electrical connections with the titanium rod electrodes are made.

Figure 2 is an enlarged cross-sectional view, at line 2 2 of one of the three-inch electrodes 2, 2. It consists of an annulus 10 of titaniumV free from solid impurities, surrounding an axial core 11 composed of solid impurity particles 12, 12 in a matrix of titanium. Core 11 is about l inch in diameter.

Example III In this example I produce an ingot in the manner described by melting and casting scrap titanium and insuring slow cooling of the ingot. In this instance the impurities are segregated in a smaller core only 1/2 inch in diameter. The ingot is made an anode as in Example I. The electrolyte, however, is magnesium chloride at 850' C. Chlorine is added to the cell during electrolysis to maintain a substantially zero back voltage. Under these conditions massive titanium is deposited on the cathode, from which it is removed and directly melted in a consumable electrode arc furnace to provide a titanium ingot having a Brinell hardness of 80.

Example IV In this example I proceed as in Example I, except that 68% titanium and containing a little carbide. I mix this with 70 lbs. of comminuted calcium. I then proceed as in ExampleA I with the tinal reduction, melting, and casting steps. The electrolysis is carried out as in Example ll using two similar ingots as the electrodes. In this example the current is reversed every minute to obtain a liner powder. This powder, which is titanium of substantially 99.9% purity, falls to the bottom of the bath, and is recovered as before.

Example V In this example I proceed as in Example I, except that the material to be agglomerated is placed in an iron tube and consolidated by tapping or ramming, and the tube is evacuated and sealed by welding. The sealed tube is heated to 1000 C. and rolled into diamond shape with a reduction in area of 50%. The tube is cooled and the tube stripped olf.A The titanium has been welded into a coherent mass and most of the slag composed of magnesium oxide and barium chloride squeezed to the end of the tube, the remainder is present in the titanium as macroscopic particles. I use this coherent titanium mass as an anode as set forth in Example I except that the anode is completely consumed. The titanium is continuously removed from the cathode as it deposits and drained to provide a metal having a minimum of included electrolyte. The particles of slag are removed from the bottom of the cell.

I claim:

1. The process of producing titanium which includes the steps of slowly cooling a body of molten impure titanium containing a minor proportion of insoluble impurities and dissolved oxygen to segregate the insoluble impurities into the core of an ingot, making said ingot an anode in a fused electrolyte of at least one salt selected from the group consisting of alkali and alkaline earth chlorides and bromides, passing a direct current from the anode to an inert cathode to produce titanium metal admixed with the electrolyte and to segregate the oxygen dissolved in the titanium metal of the anode into the core of the anode, and interrupting the electrolysis before the core begins to disintegrate.

2. The process dened in claim l, in which both electrodes are impure titanium ingots as set forth and the direction of the current is periodically reversed, whereby to produce pure titanium powder from the electrodes, and discontinuing the electrolysis without disintegration of the ingot cores.

3. The process of claim l, additionally characterized by the remelting and casting of the residual anode cores into anodes for reuse in a repetition of the process.

References Cited in the le of this patent FOREIGN PATENTS 1,064,893 France Dec. 30, 1953 

1. THE PROCESS OF PRODUCING TITANIUM WHICH INCLUDES THE STEPS OF SLOWLY COOLING A BODY OF MOLTEN IMPURE TITANIUM CONTAINING A MINOR PROPORTION OF INSOLUBLE IMPURITIES AND DISSOLVED OXYGEN TO SEGREGATE THE INSOLUBLE IMPURITIES INTO THE CORE OF AN INGOT, MAKING SAID INGOT AN ANODE IN A FUSED ELECTROLYTE OF AT LEAST ONE SALT SELECTED FROM THE GROUP CONSISTING OF ALKALI AND ALKALINE EARTH CHLORIDES AND BROMIDES, PASSING A DIRECT CURRENT FROM THE ANODE TO AN INERT CATHODE TO PRODUCE TITANIUM METAL ADMIXED WITH THE ELECTROLYTE AND TO SEGREGATE THE OXYGEN DISSOLVED IN THE TITANIUM METAL OF THE ANODE INTO THE CORE OF THE ANODE, AND INTERRUPTING THE ELECTROLYSIS BEFORE THE CORE BEGINS TO DISINTEGRATE. 